1. Field of the Invention
This invention relates in general to the construction of devices for shielding excavations such as tunnels and mine shafts and in particular to a new and useful roof support structure which includes a sill beam support and a front structure which is pivotal thereon which form together a telescopically interengageable closed working face and which provide a means for supporting a cave in shield which carries a roof cap.
2. Description of the Prior Art
The present invention deals particularly with the construction of shield-like roof supporting structures in which there is a cave in shield which is coupled to a roof cap so as to support the roof cap against the roof in a mine. The cave in shield is usually mounted so as to extend obliquely and it may be adjusted upwardly and downwardly to position the cap at the desired engagement with the roof so as to be adaptable to various seam thicknesses and the spacing of the support from the face of the workings. One known shield supporting structure of this kind includes a cave in shield which is supported on a sill beam through guide links which insure a lemniscate guidance, and the lever transmission is adjusted as to the length of the levers and pivot point positions so that during adaptation of the supporting shield to the varying seam thicknesses, the hinge point of the cap is guided along a substantially vertical line. The purpose of such an arrangement is to keep the tip of the cap at a constant distance from the base of the excavation such as the coal face in a coal mining operation. The shield supporting structure of the prior art can be vertically adjusted only during its motion in the direction of the coal face, that is while moving away from the fallen end of fragmented roof. In many cases however the broken bits of rock or coal cannot be prevented from immediately following the supporting structure so as to interfere with the operation thereof. With the known structure during the telescoping of the props the guide links swing along with the shield in the direction of the fallen-in area. Since the fragmented rocks or coal keep their contact with the supporting structure, the shield and its links which serve guides are blocked in a disadvantageous manner or at least are hindered in respect to their adjusting motions.